1. Field of the Invention
The present invention relates to a locator for locating an electrically conductive object. It is particularly suitable for measuring the position and orientation of buried underground objects such as cables and pipes.
2. Summary of the Prior Art
There is currently an increasing proliferation of underground objects such as cabling, piping, ducting etc. carrying utilities such as gas, electricity and telephone lines. Consequently it has become critical that persons involved in e.g. excavation work are aware of the location of said objects before commencing work so that unnecessary expense and inconvenience are not incurred through accidental damage.
Thus a typical target object for a locator is a cable comprising a conductive component such as metal sheathing or wiring. An electromagnetic field susceptible of detection by a locator can be produced in such a cable by e.g. the application of a signal to the cable sheathing or wiring via a suitable transmitter, or an alternating current carried by the cable.
Buried fibre-optic communication systems have especially high costs associated with their damage because of the difficulty of repairing broken fibre-optic cables and the potentially large numbers of customers who may be inconvenienced by the damage. Fibre-optic cables however usually have a protective metal sheath which can be used to make them locatable as described above.
WO-A-95-30913 disclosed a locator in the form of a ground penetration probe which had spaced antennae within the probe, each of which antennae detected electromagnetic signals from a buried underground object, such as a cable. The electromagnetic signals from the antennae were analyzed to determine the separation of the locator and the objection in the direction of the spacing of the antennae, and also in the perpendicular direction. This enabled a display to show visually the separation of the locator and the object.
In the arrangement disclosed in WO-A-95-30913, the antennae had identical aerial arrays, the aerial arrays being formed by detection coils. Although it was possible for each antenna to have an array with one horizontal and one vertical coil, WO-A-95-30913 also disclosed arrangements in which each antenna had three mutually perpendicular coils to detect magnetic fields, one coil in the direction of the spacing of the antennae, and the other two in two mutually perpendicular directions.